where \(\lambda \)  is a penalty term depending on the number of Placeholder gates in the circuit. The operation pool consists of CNOT gates between neighbouring two qubits as well as the first and fourth qubits, the Placeholder and the single qubit rotation gate Rot [1]}:
\(Rot(\phi , \theta , \omega )=R_Z(\omega ) R_Y(\theta ) R_Z(\phi )=\left[\begin{array}{cc}e^{-i(\phi +\omega ) / 2} \cos (\theta / 2) & -e^{i(\phi -\omega ) / 2} \sin (\theta / 2) \\e^{-i(\phi -\omega ) / 2} \sin (\theta / 2) & e^{i(\phi +\omega ) / 2} \cos (\theta / 2)\end{array}\right]\) 
